1. Field of the Invention
The invention relates to a television tube having a screen and a flare. The front surface of the screen facing the viewer is substantially rectangular.
Such television tubes work in accordance with the cathode ray principle. The above mentioned glass components, the screen and the flare, encompass an evacuated space. The television tube further comprises components for generating the image, particularly an electron beam canon, an electron beam deflector, a screening picture and a mask.
2. Description of the Prior Art
The border around the image area, i.e. the above mentioned front surface of the screen, is only approximately rectangular, occasionally it is approximately square as the side edges have an outward convex curve. Thus, the approximately rectangular screen has three radii: A small radius in any of the four corners, a considerably larger radius on the two narrow edges and an even larger radius on the two longitudinal edges. The contour of the screen is also maintained at its side flanks and continues on the flare. This applies to all styles, sizes and formats and to all previously known designs of the contour of the image area.
The divergence in the contour of the front surface of the screen depends on the required strength. In view of the negative pressure prevailing in the interior of the television tube the walls of the glass components have to be dimensioned accordingly so as to withstand said negative pressure. If this is not the case there is a risk of implosion which represents significant risks for the user. It is known that the resistance of hollow bodies to inside or outside forces is highest in spherical forms.
Therefore, the above mentioned divergence in the contour of the front surface of the screen from a pure rectangle, and thus also the design of the edges of the television tube, is selected so as to achieve the required strength at a given minimal wall thickness on the glass components. It is understood that the goal is to have the thinnest possible wall thickness so as to keep the weight of the television tube and its outside dimensions as low as possible.
The object of the invention is to design a television tube of the above mentioned type such that its weight and its outside dimensions can be further reduced.
The problem is solved by means of the characteristic features of the independent claims. The inventor recognized that the change from the approximately rectangular shape to a pure rectangular shape does not at all decrease the vacuum resistance of the television tube. Instead the vacuum resistance is the same as before or even higher. The edges of the front surface of the screen do not have to be strictly linear for this purpose, and accordingly, the front surface does not have to be strictly rectangular or square. The same applies to the flank surfaces of the screen and the flare as seen in cross-section vertical to the axis of the image. Whatever applies to the design of the screen also applies to the design of the flare. Therefore, according to the invention the contour of the area where the flare joins is also designed such that at least one of its four edges is at least approximately linear.
As a result of the design of the invention the weight of the screen can be reduced by up to 5%. The same applies to the weight of the flare. The overall dimensions of the television tube also decrease. The housing encompassing the television tube can be smaller because of the levelness of the flank surfaces.
The coating on the interior surface of the screen is not impaired by the design according to the invention. It can also be rectangular while the quality of the transmitted image content remains the same.
The invention partially solves the above problem already if only one of the edges of the front surface of the screen is linear or largely linear. A higher effect is achieved if two opposing edges are linear or approximately linear. An optimal effect is achieved, however, when the invention is applied to all four edges.
With regard to the degree of linearity of the individual edges, the following can be said:
The divergence from a convex curve should be considerable. This means that the radius of curvature, if there is one, is at least double that of a conventional screen. Generally, it will be such that the course of any individual edge will be perceived as linear by the naked eye. The values in practice are as follows: